1. Field of the Invention
The present invention relates to a semiconductor light emitting diode and a manufacturing method thereof and, more particularly, to a semiconductor light emitting diode having improved crystallinity and efficiency in extracting external light, and a manufacturing method thereof.
2. Description of the Related Art
In general, a light emitting diode (LED) is an element used to transmit a signal obtained by converting electric energy into energy in the form of infrared rays, visible light, or light, by using the characteristics of a compound semiconductor. The LED produces a sort of electroluminescence, and currently, an LED using a III-V compound semiconductor has been put to practical use (or has been commercialized). III nitride-based compound semiconductor is a direct transition type semiconductor, and because it can obtain a stabilized operation at a high temperature compared with an element using different semiconductor, the III nitride-based compound semiconductor is commonly applied to a light emitting element such as the LED, a laser diode (LD), or the like.
The III nitride-based compound semiconductor is generally formed on a substrate made of sapphire. However, the use of an insulating substrate such as the sapphire substrate greatly restricts the arrangement of electrodes. Namely, in the conventional nitride semiconductor LED, because electrodes are generally arranged in a horizontal direction, a current flow becomes narrow. The narrow current flow increases an operational voltage Vf of the LED, degrading current efficiency, and the LED is therefore vulnerable to electrostatic discharge. Thus, in an effort to solve the problem, a semiconductor LED in which electrodes are arranged in a vertical direction is studied.
Research into the semiconductor LED having such a vertical electrode structure is being conducted to improve the luminous efficiency, namely, the light extraction efficiency, of the semiconductor LED by forming a prominence and a depression structure on a light extraction area of the LED. The passage of light is limited in the interface of material layers because the material layers have different respective indexes of refraction. In the case of a smooth interface, when light goes from a semiconductor layer having a large index of refraction (n>1) toward an air layer having a small index of refraction (n=1), the light must be made incident to the smooth interface at below a certain angle (threshold angle) or smaller. The reason for this is because if the light is made incident at the certain angle or greater, light would be totally reflected from the smooth interface, significantly reducing light extraction efficiency. Thus, in order to solve this problem, a method of introducing a prominence and depression structure on the interface has been attempted.
One of the methods for introducing a prominence and depression structure on the interface is that a nitride semiconductor layer is stacked on a sapphire substrate with prominences and depressions and a prominent and depressed surface exposed by removing the sapphire substrate is used as a light extraction surface. However, in this method, when a semiconductor layer is formed on a growth substrate such as the sapphire substrate, the semiconductor layer may easily become defective due to the difference in a crystal constant between the substrate and the semiconductor layer, and when an additional prominent and depressed portion is formed on the semiconductor layer with the prominence and depression patterns already formed thereon through wet etching, an etchant (or an etching solution), and the like, is bound to flow to the defective portion, degrading the quality of the semiconductor layer and creating a defective product.